Conventionally, there have been well known a vehicle steering apparatus which includes a so-called power steering apparatus; i.e., an apparatus for assisting turning of turnable wheels that is performed in accordance with a steering operation of a steering wheel. Known examples of such a power steering apparatus include a hydraulic power steering apparatus which generates steering assist torque by means of a hydraulic actuator, and an electric power steering (EPS) apparatus which generates steering assist torque by means of an electric actuator such as an electric motor. In particular, in recent years, electric power steering apparatuses have drawn attention, because they can be easily mounted on a vehicle and can improve fuel consumption.
Various techniques have been proposed for power steering apparatuses so as to improve their steering performance. For example, Japanese Patent Application Laid-Open (kokai) No. 2002-145101 describes a technique relating to return control performed when a steering wheel is returned from a steered position to a neutral position. In the return control, returning torque is set such that the greater the steering angle speed, the smaller the returning torque, to thereby improve convergence at the time the steering wheel returns to the neutral position.
However, in the above-described patent document 1, since the returning torque is set in accordance with steering angle speed, a large returning torque may be applied when the steering wheel is turned. Accordingly, in such a case, there arises a problem in that the returning torque serves as resistance when the steering wheel is turned, so that the feel of steering deteriorates.